Automotive airbags are presently inflated either (1) by gas generated from a pyrotechnic charge, or (2) by gas stored under pressure, or (3) by a combination of gas obtained from both sources. As described in U.S. Pat. Nos. 4,380,346; and 5,269,861, the disclosures of which are incorporated by this reference, the amount of inflation is influenced by the ambient temperature.
When the inflation is a hot event the bag is more aggressively and more fully inflated than when the inflation is a cold or normal event. When an airbag is fully inflated in a "hot" event it may be "too full" and is therefore too hard for a passenger. Previous efforts to avoid over-inflation include the following:
(1) Provision of vents in the airbag; PA1 (2) Provision of orifices in the inflator as described in the above noted patents; PA1 (3) Provision of weakened areas in the inflator housing, e.g. as described in U.S. Pat. Nos. 4,902,036 (Column 8, Lines 10 et. seq.) and 5,346,251.
None of the above has been found to be completely satisfactory. Vents in the airbag may open too much and allow the bag to deflate to the point where it is not effective as a passenger protection. The relief afforded by orifices in the inflator is limited by the pressure buildup which takes place in the housing in which the inflator is encased because the inflator is housed in the module housing which is not provided with any means to relieve the pressure. When weakened areas in the inflator housing rupture, pieces of metal may be ejected into the interior of the vehicle and may expose the occupant to injury. Therefore a need exists for an improved means for regulating the pressure in an airbag cushion during deployment of the airbag.